Expansion clamping chuck

ABSTRACT

An expansion chuck for simultaneously chucking a tool shaft and a hollow tool part such as a beveling bush. A solid chuck body which can be chucked in the working spindle of a machine tool has in its chucking part a central receptacle bore to receive the tool shaft to be chucked as well as an external chucking face to mount the hollow tool part. An elongated toroidal chamber is arranged coaxially with the receptacle bore and the outside chucking face in the interior of the chucking part of the chuck body and is filled with an incompressible medium. Due to a hydraulic internal pressure in the toroidal chamber, both of its peripheral walls undergo elastic deformation, radially inwardly to chuck the tool shaft, and radially outwardly to chuck the hollow tool part.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention generally concerns an expansion chuck for the workingspindle of a machine tool, and more particularly such a chuck having arigid chuck body with a central receptacle bore for the shaft to bechucked, an elongated toroidal chamber which is coaxial with thereceptacle bore in the one-piece chuck body and is filled with anincompressible fluid, as well as a device for generating a hydraulicpressure in said toroidal chamber.

2. Discussion of Related Art

Expansion chucks of the type of interest here are known in variousembodiments and are mostly used for accurately centered chucking of atool shaft such as the shaft of a drill or a milling cutter to securethese tools in the working spindle of a corresponding machine tool. Withthese types of hydraulic expansion chucks, which are known from GermanUtility Model 9,411,260, or from unexamined German Patent 2,700,934, forexample, the toroidal chamber formed in the body of the chuck isbordered on the inside radially by a so-called expansion sleeve whichundergoes elastic deformation radially toward the inside when hydraulicpressure is applied in this toroidal chamber, thereby securely grippingon all sides the tool shaft inserted into the receptacle bore.

A Tendo brochure from Fritz Schunk GmbH describes a hydraulic expansionchuck for tool sharpening and grinding machines, where the toroidalchamber filled with the incompressible liquid is deformed in thecylindrical chucking part of the chuck body, where the radial insidewall of this toroidal chamber has a relatively small wall thickness andundergoes deformation radially toward the inside under the hydraulicpressure in the toroidal chamber to chuck the tool shaft. After thecentral receptacle bore for the tool shaft there is a threaded bolt in across hole having a polygonal opening on its end which is accessiblefrom the outside for insertion of a tool and having an outside thread inthis enlarged end head which engages with an inside thread worked intopart of this cross hole. At the other end of the shaft of this bolt,there is a piston which is moved back and forth by a screw action of thebolt in a cylindrical space with a sealing effect. This cylindricalspace communicates with the toroidal chamber through an axially parallelchannel in the body part of the chuck. By turning the bolt using a toolinserted from the outside, the internal pressure in the toroidal chambernecessary for the chucking operation and for the elastic deformation ofthe inside wall is created by means of the corresponding pistondisplacement in the cylinder filled with incompressible liquid. However,this expansion chuck as well as others that are already known weredesigned only for chucking a one-piece part such as the shaft of a tool.

On the other hand, so-called expansion mandrels for centrally securinghollow cylindrical work pieces for lathing, for example, are alreadyknown, where a narrow toroidal chamber which determines the respectivechucking range is formed in a corresponding recess in the body of themandrel which is limited toward the outside radially by an expansionsleeve. This external expansion sleeve is expanded radially outward,thus chucking the work piece placed previously on the mandrel, due tothe buildup of an internal hydraulic pressure in this toroidal chamberfilled with incompressible liquid.

German Patent 743,530 describes a chucking device for machine toolshaving a double-walled chucking sleeve for securing a hollow cylindricaltool on a shaft. The chucking sleeve is designed with a double wall andis securely attached to one end with a toroidal rotating body whichaccommodates a device for producing a hydraulic pressure in theelongated toroidal chamber of the chucking sleeve. Due to this hydraulicpressure in the toroidal chamber, the two peripheral walls of thedouble-walled chucking sleeve undergo elastic deformation with a radialinward and radial outward force, and are brought into pressure contactwith the outside surface of the shaft and with the inside surface of thehollow cylindrical tool. Simultaneous chucking of two tools is neitherprovided here nor is it readily feasible.

International patent publication WO 93/18880 describes a hydraulic workholding bushing for chucking lathe tools in the tool receptacles of arevolver head having a thin-walled hollow cylindrical chucking part anda ring body connected to it. An elongated toroidal chamber communicateswith a device arranged in the ring body to generate an internalhydraulic pressure. The two peripheral walls of the toroidal chamber arethin and undergo elastic deformation due to the hydraulic pressure inthe toroidal chamber, so they are brought into pressure contact with theoutside wall of the lathe tool and against the inside wall of the toolreceptacle.

Finally, it is known from German Patent 1,552,257 and German UtilityModel 9,411,260 that the shaft of a tool can be chucked in an expansionsleeve positioned separately in the chuck and additionally secured byteeth or by claw engagement, for example, to prevent twisting.

SUMMARY OF THE INVENTION

The object of the present invention is to create an expansion chuck thatcan be secured in the working spindle of a machine tool which permitsnot only chucking of a tool shaft but also centered chucking of a hollowcylindrical part, especially a beveling bushing, in a simple andaccurate manner.

This invention makes it possible for the first time in a technicallysimple and inexpensive manner not only to chuck a solid cylindrical partsuch as the shaft of a tool, but also to additionally chuck a hollowcylindrical part such as another tool, a measurement gauge holder or thelike, with high strength and accurate centering in a predetermined axialposition on the longitudinal axis. Since the hydraulic pressuregenerated in the interior of the toroidal chamber also acts radiallyinwardly as well as radially outwardly, an elastic deformation of thebordering wall of the toroidal chamber radially on the inside andradially on the outside occurs simultaneously, using a single internalpressure generating operation, so that two separate parts can be chuckedsimultaneously without requiring any additional measures. When using twoseparate tools such as a shaft drill and a ring-shaped or socket-shapedbeveling tool, a hole can be drilled in a work piece and a bevel can becut at the entrance of the bore hole in a single operation. When using asocket-shaped tool with a suitable cutting geometry on the end face,so-called differential bore holes can also be produced in a singleoperation. In order to be able to transmit even a high torque to theadditional tool without interference, another aspect of the presentinvention is characterized in that the hollow cylindrical part or thesocket-shaped part of the additional tool is secured in a form-fittingmanner to prevent it from twisting on the body of the chuck. Atechnically simple and inexpensive method of rotational fixationconsists, for example, of a projection shaped on a rear edge of thesocket-shaped part or a strap which is fitted into a suitably shapedaxial groove in the chuck body so that it is longitudinally displaceableand allows axial adjustment of the socket-shaped part or the bevelingbushing. To accurately set the length of the additional tool which ischucked from the outside and optionally make a mutual adjustment of thetwo tool positions, the axial operating position of the additional toolon the chuck body can be adjusted with a high degree of precisionaccording to another aspect of this invention. Spacer bushings haveproven to be especially suitable as adjusting means, which are screwedonto the rear end section of the socket-shaped part of the additionaltool before the latter is chucked and are supported with their end edgeon a ring stop on the chuck body.

To have a controlled influence on the chucking forces directed radiallyoutwardly and radially inwardly, the thickness of the inside wall andthe outside wall of the toroidal chamber is varied over their lengthaccording to another aspect of the present invention, which isaccomplished in practical terms by means of a slightly conicalarrangement of the toroidal chamber in the chuck body or through acurve-shaped or stepped course of the toroidal chamber in thelongitudinal direction.

According to an additional aspect of the present invention, the outsidewall of the chucking part of the chuck body may have elongated areas ofa reduced wall thickness in alternation with thicker wall areasdistributed uniformly over the circumference. The thinner wall areas maybe longitudinal grooves and they cause the thicker wall areas to bepressed with a greater chucking force against the cylindrical insidesurface of the sleeve. It is also possible to design the outside wall ofthe chucking part of the chuck body and the inside wall of the sleeve ofthe additional tool as having a polygonal profile, for example, ahexagonal cross section, thus resulting in an additional stable twistlocking effect of the two parts during and after the chucking operation.

If an additional form-fitting connection of the sleeve on a chuck or achucking mandrel by means of a screw thread is desired, a twist lockingmeans may be achieved by widening the area of the thread by hydraulicmeans, so that the threads of the two parts are pressed together under ahigh force, thereby eliminating the play necessary for the screwingoperation.

BRIEF DESCRIPTION OF THE DRAWING

The objects, advantages and features of this invention will be morereadily apparent from the following description, when read inconjunction with the accompanying drawing, wherein:

FIG. 1 is a partial sectional side view of an expansion chuck with theshaft chucked in it and with a hollow cylindrical beveling tool chuckedin it in a partially cut away side view, in accordance with theinvention;

FIG. 2 is a partial sectional side view of another expansion chuck inaccordance with the invention, with a twist locking means on thebeveling tool;

FIG. 2a is a partial top view of the twist locking means, taken fromposition X in FIG. 2;

FIG. 3 is a sectional view of the expansion chuck of FIGS. 1 and 2,taken through cutting plane II—II;

FIG. 4 is another embodiment of the expansion chuck of the invention ina schematic cross sectional diagram;

FIG. 5 is an alternative embodiment of the expansion chuck of theinvention in a schematic axial diagram; and

FIG. 6 is a further alternative embodiment of the expansion chuck of theinvention in a schematic axial diagram.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As FIG. 1 shows, the expansion chuck consists of a chuck body 1 which ischucked in a known manner in the receptacle device (not shown) of arotationally driven working spindle of a machine tool with its left endpart 2 in the form of a truncated cone. A hollow cylindrical chuckingpart 4, which is shown with hatching in the upper part of FIG. 1 andwith dotted lines in the lower part of the figure, is connected by aconical section to central part 3 with a larger diameter of preferablysolid chucking body 1 which is designed in one piece. Furthermore,central receptacle bore 5 into which cylindrical shaft 6 here, forexample, the shaft of a drilling tool, is inserted in chuck body 1.

Narrow toroidal chamber 7 is provided inside chucking part 4 of chuckbody 1 so that it is axially centered and is coaxial with receptaclebore 5, whose length corresponds approximately to the required chuckingrange. Toroidal chamber 7, which is closed at one end, is bordered onthe inside radially by inside wall 8 and on the outside radially byoutside wall 9, both of which are parts of chuck body 1. The wallthickness of outside wall 9 is approximately 1.5 to 3 times greater thanthe wall thickness of inside wall 8. Toroidal chamber 7 communicateswith cylindrical space 11 by way of channel 10 (shown with dotted lineshere) in chuck body 1, the cylindrical space being bordered by controlelement 12 at one end consisting in a known way of a piston, a shaft andan outside threaded section into which a lathe tool can be inserted.Cylinder 11, channel 10 and toroidal chamber 7 are completely filledwith a generally incompressible liquid. Peripheral surface 13 of outsidewall 9 of chucking part 4, like the inside peripheral surface of insidewall 8, is designed as a precision machined cylindrical chucking face. Abushing-shaped additional tool 14 has been pushed onto peripheral face13 of outside wall 9 and it has cutting plate 15 on its wedge-shapedright end section, which in the present case is a beveling tool forbeveling the bore hole end produced with the drill. By means ofadjusting ring 16, the axial position of beveling tool 14 with respectto the drill tip or chucking part 4 of chuck body 1 can be adjusted.Adjusting ring 16 is screwed onto the end section of bushing-shapedadditional tool 14 by means of an inside thread and is supported on theconical section of chuck body 1 as shown here. By twisting adjustingring 16 the precise axial position of additional tool 14, 15 withrespect to the position or length of the main tool is adjusted beforethe chucking operation.

For simultaneous chucking of tool shaft 6 in receptacle bore 5 plusadditional tool 14 on outside chucking surface 13 of chucking part 4, ahigh pressure is exerted on the liquid contained in cylinder 11 byscrewing in control element 12 into the threaded bore (by means of itspiston), and this pressure is transmitted via channel 10 into toroidalchamber 7. This hydraulic pressure causes an elastic bulging of insidewall 8 until it comes into pressure contact with the outside of shaft 6while at the same time there is a radial bulging of outside wall 9 untilit comes into pressure contact with the inside wall of socket-shapedbeveling tool 14. Thus two separate parts, namely tool shaft 6 and alsothe socket-shaped or bushing-shaped part of additional tool 14 arechucked at the same time by a single operation of control element 12,thereby achieving the precise centering of two tools 6 and 14 which ischaracteristic of the expansion chuck principle.

The embodiment according to FIG. 2 corresponds largely to the embodimentaccording to FIG. 1 as described above, with the same parts beinglabeled with the same reference numerals. If greater torques are to betransmitted from the chuck to additional tool 14 and if outside wall 9has a greater wall thickness, an additional form-fitting twist lockingmeans is provided to suppress any additional slippage between chuck body1 and additional tool 14 which is under stress in chucking. Thisadditional twist locking means may be provided in various ways throughappropriate shaping of the components such as cotter and keyway joints,and non-round cross sections, among others. With the embodimentdiagrammed in FIG. 2, axial projection or tab 17 is molded onto thesocket-shaped part of additional tool 14, engaging in cutout 18 inconical transitional section 3 a of chuck body 1 in disk seating. Thewidth of dimensionally stable tab 17 corresponds approximately to thewidth of cutout 18 and its length is smaller than the length of thecutout to prevent collisions in the axial adjustment of additional tool14.

In the embodiments according to FIGS. 1 and 2, chucking face 13 isdesigned with a continuous cylindrical shape on outside wall 9, but inthe variants according to FIG. 4 outside wall 19 has a different crosssection with thicker and thinner areas 20, 22 which are distributedaround the circumference at the same angular offset in an expedientmanner and extent throughout the entire length of the effective chuckingarea. Areas 22 of reduced wall thickness are formed in the embodimentillustrated in the upper half of FIG. 4, labeled “a,” by externallongitudinal grooves 21 in outside wall 19.

As shown in the lower half of FIG. 4, labeled “b,” chucking part 4 mayhave an outside hexagonal cross section, and bushing 14 may have aninside hexagonal cross section, thus also achieving a form-fitting twistlocking effect in addition to an increased chucking effect in certainareas of the wall.

With the embodiments illustrated in FIGS. 5 and 6, the chucking forcesexerted by chucking part 4 on inside shaft 6 and on outside bushing 14vary over the length of the chucking zone, which offers advantages incertain applications. The variant according to FIG. 5 has toroidalchamber 7 a running conically in the interior of chucking part 4,causing a uniform variation in wall thickness of inside and outsidebordering walls 8 a and 9 a. Due to the greater expansion of thinnerdividing wall 8 a in the right part of FIG. 5, greater tolerances withrespect to shaft 6 can be bridged or tolerated in this section. The samething is also true in the left part of FIG. 5 for outside wall 9 a whichis thinner here with respect to bushing 14.

In the embodiment according to FIG. 6, toroidal chamber 7 b consists ofthree sections, namely a left sided section radially on the outside, acentral conical section and a right sided section radially on theinside. Since the hydraulic pressure in toroidal chamber 7 b is equalover its length, this results in different chucking effects accordinglyin the two end sections owing to the different wall thicknesses ofinside and outside walls 8 b and 9 b. In addition, with this embodimentthe strength of the connection between chucking part 4 and bushing 14 isfurther increased by screwing the two parts together by means of thread23. Due to the chucking action of thinner outside wall 9 b, the usualthread play is eliminated and an additional securing effect is achieved.The middle section may also run radially.

This invention is not limited to the embodiments illustrated here anddescribed above. For example, instead of beveling at tool 14, otheraccessory parts may also be used for certain suitable purposes. Thesecould be for simultaneously performing additional machining operations,for measurement purposes, and for supplying coolant media to the workingarea of the main tool, among others. Furthermore the inside wall and theoutside wall of the toroidal chamber may also have the same wallthickness, and the inside wall may also be consistently thicker than theoutside wall, so that together with its internal chucking face itundergoes less expansion than the outside wall. It has been found thatexpansion adequate for chucking of the thicker wall can also be achievedwith wall thickness ratios of more than 1 to 10. Furthermore the wallthickness of one or both walls may be varied gradually or incrementallyin the longitudinal direction so as to result in toroidal zones ofdifferent expansion stresses.

In view of the above description, it is likely modifications andimprovements will occur to those skilled in this technical field whichare within the spirit and scope of the claims. Thus the invention is tobe limited only by the accompanying claims and equivalents.

What is claimed is:
 1. An expansion chuck for simultaneously chucking atool shaft and a hollow tool part, the expansion chuck comprising: asolid chuck body which can be chucked in the working spindle of amachine tool, said chuck body having a central receptacle bore formingan inside peripheral wall in its chucking part to receive the tool shaftto be chucked, and an outside chucking face on an outside peripheralwall to hold the hollow tool part; an elongated toroidal chamber formedin the interior of said chucking part of said chuck body, said toroidalchamber being arranged coaxially with said receptacle bore and with saidoutside chucking face; and apparatus for generating a hydraulic internalpressure on said toroidal chamber so that said two peripheral wallsundergo elastic deformation due to internal hydraulic pressure in saidtoroidal chamber acting radially toward the inside for chucking the toolshaft and radially toward the outside for chucking the hollow tool part.2. The expansion chuck according to claim 1, and further comprisingmeans on said hollow tool part to prevent twisting on said chuck body.3. The expansion chuck according to claim 2, wherein said means toprevent twisting comprises at least one axially projecting tab on saidhollow tool part as a twist locking device which engages in at least onerecess in said chuck body with a predetermined longitudinal play.
 4. Theexpansion chuck according to one of claims 1 through 3, wherein saidhollow tool part is a beveling bushing having a forward, conicallytapered end part on which is mounted at least one beveling blade.
 5. Theexpansion chuck according to one of claims 1 through 3, wherein theaxial position of said hollow tool part on said chucking part of saidchuck body is adjustable.
 6. The expansion chuck according to claim 5,and further comprising an adjusting ring for adjusting the axialposition of said hollow tool part on said chuck body.
 7. The expansionchuck according to one of claims 1 through 3, wherein the thickness ofsaid outside wall is less than, equal to or greater than the thicknessof said inside wall.
 8. The expansion chuck according to one of claims 1through 3, wherein said outside wall has areas of a reduced wallthickness running longitudinally and distributed around thecircumference in alternation with thicker wall areas.
 9. The expansionchuck according to one of claims 1 through 3, wherein the thicknesses ofsaid outside wall and said inside wall vary over the length of saidtoroidal chamber.
 10. The expansion chuck according to one of claims 1through 3, wherein said bushing engaged on said chucking part is screwedto said chucking part in the chucking area.
 11. The expansion chuckaccording to one of claims 1 through 3, wherein said apparatus forgenerating hydraulic pressure in said toroidal chamber has a manuallyoperated control element including a piston, which is arranged in across hole in said chuck body so that it is manually adjustable and saidpiston generates a hydraulic pressure in a cylindrical chamber whenadjusted, said pressure being transmitted to said toroidal chamberthrough a channel.
 12. The expansion chuck according to one of claims 1through 3, wherein said apparatus for generating hydraulic pressure insaid toroidal chamber has an external pressure shaft connected bychannels in said chuck body to said toroidal chamber.